For several reasons, it is interesting to know how a combustion engine behaves over time. One reason may be that one wants to monitor in which engine speed area the engine has been operating and which torque has been requested from it, for example to predict when the engine needs to be serviced or to predict the total service life of the engine.
U.S. Pat. No. 6,334,085 describes a device for data processing which is used to keep a track on how long the engine has been operating with different loads and engine speed, and based on this information, for example, to estimate the engine's service life. As a measure of the load, a difference between engine speed under load and no load speed is used, and a matrix is created with different sections for storage of information. Each section is associated with specific intervals of values for the above mentioned difference and for the engine's engine speed with no load. The time which the engine spends in a certain section is logged in the matrix.
Other aspects of a combustion engine's behavior over time may, however, also be interesting to be aware of, for example in order to detect differences from the expected behavior. In particular, this applies to the torque generated by the engine, which should not change over time in relation to the torque requested from the engine. If the generated torque over time begins to differ from the requested torque, this means that the combustion engine is not functioning as intended, which may be a sign that it needs to be repaired or serviced. For example, the generated torque may decrease in relation to the requested torque if the fuel injectors are clogged and need to be cleaned.
Also, with respect to other operating characteristics such as charge air pressure, exhaust back pressure, mass flow, fuel pressure, fuel consumption, engine temperature, catalyst temperature, auxiliaries engagement rates, turbine speed, throttle position etc., it may be important to know that these do not change over time and begin to differ from expectations. Several of these operating characteristics are difficult and/or expensive to measure exactly, and it is therefore of interest to find a way of detecting differences from expectations without having to measure the actual values.
WO2010/073111 describes a method to monitor the fuel consumption in a combustion engine. The fuel consumption is measured and associated with the engine's engine speed and torque at the actual measuring time. The measuring value is saved in a matrix, which at predetermined points in time is updated by having the most recently measured fuel consumption value saved in association with the current engine speed and torque, or by an average of a number of measured values for the fuel consumption at the current engine speed and torque being saved in the matrix. The matrix is thus continuously updated, since the most recently obtained value relating to fuel consumption replaces a previously saved value. This method may therefore not be used to determine how the fuel consumption has varied over time.